I've been told by a BMW advisor that 3.0 is more reliable. You may ask for a quote for an extended warranty and compare the costs for 3.0 vs. 4.8. That's another indicator. Obviously, it has less power than 4.8, but a test drive will tell if it's worth it.

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2011 BMW 740i
2011 Toyota Sienna Limited
2008 X5 3.0 Space Gray (sold)